Influence of Urotropin on the Precipitation of Iron Oxides from FeCl3 ...

1024 A. ŠARI] ET AL.
The FT-IR spectra were recorded using a Perkin-Elmer spectrometer 2000 model.
The IRDM (Infrared Data Manager) program, obtained by Perkin-Elmer, was
used to process the recorded spectra.
Mössbauer spectra were recorded using standard equipment and a 57Co source.
Mathematical deconvolutions <strong>of</strong> the recorded spectra were performed using a standard
procedure.
X-ray powder diffraction measurements were performed using the Philips diffractometer
MPD 1880 model (Cu-K radiation, graphite monochromator and proportional
counter).
The size and shape <strong>of</strong> the particles were monitored by transmission electron microscopy
(Opton EM-10 model). Before the transmission electron microscopic observation,
the powders were dispersed in doubly distilled water by ultrasonic waves
and then a drop <strong>of</strong> the dispersion was placed on a copper grid, previously covered by
a polymer film.
RESULTS AND DISCUSSION
FT-IR Spectroscopy
The present work shows high potentials <strong>of</strong> FT-IR spectroscopy in monitoring
phase changes in the iron oxide precipitates. This is illustrated by
the FT-IR spectra shown in Figures 1 to 6.
Figures 1 and 2 show the FT-IR spectra <strong>of</strong> samples C1 to C10, prepared
by varying the concentration <strong>of</strong> FeCl3 , and at an initial concentration <strong>of</strong>
0.025 M urotropin. After 24 hours <strong>of</strong> aging the precipitation system, prepared
from 0.005 M FeCl3 solution, a mixture <strong>of</strong> -Fe2O3 and -FeOOH was
observed. The IR bands at 563 and 464 cm –1 are due to the presence <strong>of</strong>
-Fe2O3 , whereas the bands at 896 and 799 cm –1 are typical <strong>of</strong> -FeOOH. At
a concentration <strong>of</strong> 0.02 M FeCl3 , the -FeOOH phase appeared in sample
C3, as concluded on the basis <strong>of</strong> a new and strong IR band at 694 cm –1 . The
origin <strong>of</strong> IR bands corresponding to -FeOOH, -FeOOH and -Fe2O3 will
not be discussed here because adequate assignations <strong>of</strong> these IR bands were
presented in earlier papers. 18,21–23 At concentrations <strong>of</strong> 0.05 and 0.3 M FeCl3 ,
the presence <strong>of</strong> -FeOOH, as a single phase in samples C4 and C5, is observed.
These phase changes in the precipitates were associated with the
pH change in the mother liquor from 7.61 to 0.78. After 7 days <strong>of</strong> aging the
precipitation systems C6 to C10, the main change was observed in the FT-
IR spectrum <strong>of</strong> sample C8, precipitated from 0.02 M FeCl3 . The fraction <strong>of</strong>
the -FeOOH phase (IR bands at 896 and 800 cm –1 ) significantly increased,
whereas the -FeOOH phase was absent. The pH <strong>of</strong> the mother liquor decreased
from 5.55 to 5.29. This shows that the fraction <strong>of</strong> -FeOOH, formed
at the beginning <strong>of</strong> the precipitation process, dissolved after 7 days.